[Nauty] Fw: Filters graphs with diameters greater than 2 and less than 4

Sat Sep 30 23:26:04 AEST 2023

Hello,

Thank you for your reminder. Your first way is nice.  I tried your translate function, but it didn't work for me. If you have specific steps, please let me know. Anyway, I have two other methods that seem pythonic. 

One is to use regular expressions.
```
import re
import networkx  as nx
char_map = {
    '\a': r'\a',
    '\b': r'\b',
    '\c': r'\c',
    '\f': r'\f',
    '\n': r'\n',
    '\r': r'\r',
    '\t': r'\t',
    '\v': r'\v',
    '\'': r'\'',
    '\"': r'\"'
}

pattern = re.compile('|'.join(re.escape(key) for key in char_map.keys()))
line = 'ihChWC@?gE_@?@?A_ at g?@??C??j?@l??E??Ao??\???m??@I??DF??E`O??GM??@?g??S\@o?@g at O??G?w??C?I??D?@o?@g?D???_?M??@??I??D??FK?E_?@Q??G??N??@???CPCOaG\a??'
line1 = pattern.sub(lambda x: char_map[x.group(0)], line)
G = nx.from_graph6_bytes(line1.encode())
print(G)
```
Another way to write it.

```
import functools
import networkx  as nx
char_map = [
    ('\a', r'\a'),
    ('\b', r'\b'),
    ('\c', r'\c'),
    ('\f', r'\f'),
    ('\n', r'\n'),
    ('\r', r'\r'),
    ('\t', r'\t'),
    ('\v', r'\v'),
    ('\'', r'\''),
    ('\"', r'\"')
]
def replace_chars(s, mapping):
    return functools.reduce(lambda s, replacement: s.replace(*replacement), mapping, s)
line = 'ihChWC@?gE_@?@?A_ at g?@??C??j?@l??E??Ao??\???m??@I??DF??E`O??GM??@?g??S\@o?@g at O??G?w??C?I??D?@o?@g?D???_?M??@??I??D??FK?E_?@Q??G??N??@???CPCOaG\a??'
line1 = replace_chars(line, char_map)
G = nx.from_graph6_bytes(line1.encode())
print(G)
```

By the way, I made some improvements to the code before, such as passing the filter through a pipe directly from geng instead of exporting it to a file (using universal_newlines=True).

import subprocess
import sys
import networkx  as nx
import functools
escape_dict={'\a':r'\a',
             '\b':r'\b',
             '\c':r'\c',
             '\f':r'\f',
             '\n':r'\n',
             '\r':r'\r',
             '\t':r'\t',
             '\v':r'\v',
             '\'':r'\'',
             '\"':r'\"'}

process = subprocess.Popen(['geng', '19', '22', '-b'], stdout=subprocess.PIPE, universal_newlines=True)
count = 0
for line in process.stdout:
    line=line.strip()
    #Eliminate the impact of escape characters
    line=''.join((escape_dict[x] if x in escape_dict else x) for x in line)
    G = nx.from_graph6_bytes(line.encode())    
    if  len(nx.max_weight_matching(G))==4:
        count+=1
        sg=nx.to_graph6_bytes(G)
        cleaned_g6string = sg[10:-1].decode()
        print(cleaned_g6string)
print(count,"graphs written to stdout")

One of the more interesting things is when does geng produce graphs with \ characters. I've been looking to check if my code is working.

Best wishes.
Licheng.

在 2023-09-30 18:54:24，keith.briggs at bt.com 写道：

That code is quite unpythonic.  You should not use try...except for checking keys in dictionaries. It could be done in one line like this:

line=''.join((escape_dict[x] if x in escape_dict else x) for x in line)

But much better is just to use the built-in string translate method:

line=line.translate(r'\a\b...','\a\b...')

Also, count=count+1 should be count+=1.

Keith 

From: lczhangmath <lczhangmath at 163.com>
Sent: Saturday, September 30, 2023 01:25
To: Briggs,KM,Keith,TUD2 R <keith.briggs at bt.com>
Cc: nauty at anu.edu.au <nauty at anu.edu.au>
Subject: Re:Re: Re:Re: Re:Re: [Nauty] Fw: Filters graphs with diameters greater than 2 and less than 4

Dear Keith, 

Fortunately, the problem with escape characters here can now be solved in python. We always want graph6 strings involving \ not escaped, I attach the full code below. 

import subprocess
import sys
import networkx  as nx
escape_dict={'\a':r'\a',
             '\b':r'\b',
             '\c':r'\c',
             '\f':r'\f',
             '\n':r'\n',
             '\r':r'\r',
             '\t':r'\t',
             '\v':r'\v',
             '\'':r'\'',
             '\"':r'\"'}

def raw(text):
    """Returns a raw string representation of text"""
    new_string=''
    for char in text:
        try: 
            new_string += escape_dict[char]
        except KeyError: 
            new_string += char
    return new_string

completed_process = subprocess.run(['geng', '9', '8', '-b', '-c'], stdout=subprocess.PIPE, text=True)
output_lines = completed_process.stdout.splitlines()
count = 0
for line in output_lines:
    line=line.strip()
    #Eliminate the impact of escape characters
    line=raw(line)
    G = nx.from_graph6_bytes(line.encode())    
    if nx.diameter(G)<=4 and  nx.radius(G)>=2:
        count=count+1
        sg=nx.to_graph6_bytes(G)
        cleaned_g6string = sg[10:-1].decode()
        print(cleaned_g6string)
print(count,"graphs written to stdout")

Also see the link: https://stackoverflow.com/questions/12605090/how-to-prevent-automatic-escaping-of-special-characters-in-python

If you have any further questions, please feel free to contact me. Thank you again for reminding me of the previous question.

Best wishes,
Licheng.

在 2023-09-29 22:56:40，keith.briggs at bt.com 写道：

r'...' is for literal strings only.

Keith 

From: lczhangmath <lczhangmath at 163.com>
Sent: Friday, September 29, 2023 3:13:31 pm
To: Briggs,KM,Keith,TUD2 R <keith.briggs at bt.com>
Cc: nauty at anu.edu.au <nauty at anu.edu.au>
Subject: Re:Re: Re:Re: [Nauty] Fw: Filters graphs with diameters greater than 2 and less than 4

It's off-topic in a sense, but it doesn't seem to be too far off, and there might be problems with calling these programs from python scripts. Although I don't see much of a problem for the moment, for the small graphs from geng, even if I don't replace \ to \\. You said r+string, I think that's right, but I have already got the string in the pipeline and it can't append r. This is frustrating.

Licheng.

在 2023-09-29 22:01:01，keith.briggs at bt.com 写道：

This is getting off-topic, but in python it's much safer to use r-strings when you have backslashes in the string, like this: r'\'.

Keith 

From: lczhangmath <lczhangmath at 163.com>
Sent: Friday, September 29, 2023 2:50:59 pm
To: Briggs,KM,Keith,TUD2 R <keith.briggs at bt.com>
Cc: nauty at anu.edu.au <nauty at anu.edu.au>
Subject: Re:Re: [Nauty] Fw: Filters graphs with diameters greater than 2 and less than 4

| |

| |
Hello, Keith
You are right. May be I need write line = line.replace("\\", "\\\\").  I'm worried about the effect of escape characters, for example, 

import networkx  as nx
line="ihChWC@?gE_@?@?A_ at g?@??C??j?@l??E??Ao??\???m??@I??DF??E`O??GM??@?g??S\@o?@g at O??G?w??C?I??D?@o?@g?D???_?M??@??I??D??FK?E_?@Q??G??N??@???CPCOaG\a??"
G = nx.from_graph6_bytes(line.encode())

It gives a error:  File "C:\Users\asus\AppData\Roaming\Python\Python310\site-packages\networkx\readwrite\graph6.py", line 118, in from_graph6_bytes
    raise NetworkXError(
networkx.exception.NetworkXError: Expected 861 bits but got 858 in graph6

So I replace all \\ to \\\\ But it remains wrong. 

import networkx  as nx
line="ihChWC@?gE_@?@?A_ at g?@??C??j?@l??E??Ao??\???m??@I??DF??E`O??GM??@?g??S\@o?@g at O??G?w??C?I??D?@o?@g?D???_?M??@??I??D??FK?E_?@Q??G??N??@???CPCOaG\a??"
G = nx.from_graph6_bytes(line.encode())

Because the lower \a in the string is treated as x07 in advance. I can't do anything about it. I know that we can add a prefix r to the string and leave it as it is, without escaping. As follows:

import networkx  as nx
line=r"ihChWC@?gE_@?@?A_ at g?@??C??j?@l??E??Ao??\???m??@I??DF??E`O??GM??@?g??S\@o?@g at O??G?w??C?I??D?@o?@g?D???_?M??@??I??D??FK?E_?@Q??G??N??@???CPCOaG\a??"
G = nx.from_graph6_bytes(line.encode())
print(G)

Output: Graph with 42 nodes and 138 edges

But we have exported the string, it is already escaped (completed_process.stdout.splitlines()), I can't add the prefix r in front, do you have any good ideas? Of course, it seems that there are no annoying characters like \ in graphh6 when there are fewer vertices. 

Best wishes,
Licheng 

在 2023-09-29 15:26:10，keith.briggs at bt.com 写道：

The line.replace statement won't do anything, since you throw away the result.

Keith 

From: Nauty <nauty-bounces at anu.edu.au> on behalf of lczhangmath <lczhangmath at 163.com>
Sent: Friday, September 29, 2023 6:37:51 am
To: nauty <nauty at anu.edu.au>
Subject: [Nauty] Fw: Filters graphs with diameters greater than 2 and less than 4

[
---- Forwarded Message ----
| From | lczhangmath<lczhangmath at 163.com> |
| Date | 09/29/2023 13:08 |
| To | Brendan McKay<brendan.mckay at anu.edu.au> |
| Subject | Re:Re: [Nauty] Filters graphs with diameters greater than 2 and less than 4 |
Dear  Prof. Brendan,

Thank you for informing me of the overlooked option. Before you informed me, I wrote a Python script. Of course, this script can combine some parameter filtering, a bit like the SageMath call. But I am very looking forward to your handling in C language.

Python script:

import subprocess
import sys
import networkx  as nx
completed_process = subprocess.run(['geng', '9', '8', '-b', '-c'], stdout=subprocess.PIPE, text=True)
output_lines = completed_process.stdout.splitlines()
count = 0
for line in output_lines:
    line=line.strip()
    #Eliminate the impact of escape characters
    line.replace("\\", "\\\\")
    G = nx.from_graph6_bytes(line.encode())
    if nx.diameter(G)<=4 and  nx.radius(G)>=2:
        count=count+1
        sg=nx.to_graph6_bytes(G)
        cleaned_g6string = sg[10:-1].decode()
        print(cleaned_g6string)
print(count,"graphs written to stdout")

Best wishes,
Licheng Zhang.

在 2023-09-28 20:19:36，"Brendan McKay" <Brendan.McKay at anu.edu.au> 写道：
>Hi Licheng,
>
>geng -c 7 | pickg -Z2:4
>
>You can use a range like that for all numerical parameters.  You can
>also use -Z:4 for <=4 and -Z2: for >=2.
>
>I'll answer your earlier question tomorrow.
>
>Brendan.
>
>On 28/9/2023 9:43 pm, lczhangmath wrote:
>> Hello,
>>
>>
>> The second question in my email, titled "matching number and operations between parameters", contains this question, and I recount it in detail here.
>>
>>
>> As with equations, we sometimes need to filter for cases that satisfy a parametric inequality. For example, I
>> would like to get all 7-vertex  graphs with diameter k where k is greater than or equal to 2 and less than or equal to 4.
>>
>>
>> At this time, either I use the external script (e.g. sagemath) or I run the following shell script, but the sctipt always repeats the execution of geng, so the efficiency is not high.
>>
>>
>> for i in {2..4}
>> do
>>      echo "Running geng 7 -c | pickg -V -Z$i"
>>      geng 7 -c | pickg -Z$i >> output.txt
>> done
>>
>>
>>   I don't know where I can change the source code to achieve this.
>>
>>
>>
>>
>> Best regards,
>> Licheng Zhang
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